The present invention relates to heavy-duty trailers used for over-the-road hauling of heavy equipment of various kinds, such as dozers, tractors, fork lifts, trucks and other vehicles. More particularly, it relates to that category of trailers known as xe2x80x9ctail trailersxe2x80x9d or xe2x80x9chydraulic tail trailersxe2x80x9d wherein a hinged rearmost portion of the trailer can be lowered to the ground or raised to a dock to serve as a ramp for loading and unloading purposes.
A wide variety of tail trailers are currently available. However, for the most part conventional tail trailers have complicated tail constructions that reduce reliability, increase maintenance requirements, increase down time during actuation and de-actuation of the tail, and increase the level of operator skill required. Increased costs due to the use of various latches, linkages and numerous hydraulic cylinders are also a significant negative factor.
Furthermore, the industry has thus far been unable to provide the public with a commercially successful tail trailer in which the load-supporting ground wheels of the trailer are located directly beneath the tail during over-the-road travel so as to obtain the significant operational advantages associated with that relationship. Instead, the common practice in the industry has been to locate the supporting undercarriage ahead of the hinge point of the tail so that the tail hangs out far beyond the wheels of the undercarriage. Among other things, this arrangement decreases the pay load available for the trailer because it increases the weight on the rear axle of the tractor-trailer rig while reducing the weight on the front axle at the tractor itself. Furthermore, without the undercarriage directly beneath the tail during roading, loads on the tail must be borne by hydraulic cylinders or other contrivances that operate the tail.
Accordingly, an important object of the present invention is to provide an improved tail trailer that overcomes the shortcomings of currently available tail trailers. In this regard, the present invention provides a simple, easy-to-operate tail trailer which can be quickly converted between loading and transport modes, and yet the supporting undercarriage and its ground wheels are located back under the tail in load supporting relationship therewith during over-the-road travel. While the tail can be quickly and easily lowered to the ground for using the tail as an upramp for loading equipment from the ground, it can also be easily raised up beyond a level condition to dock-height so as to serve as a downwardly inclined loading ramp from the dock, thus rendering the trailer extremely versatile. Notwithstanding the foregoing features, the trailer is provided with a sturdy bumper system beneath the tail that protects against accidental drive under situations by automobiles and the like.
Actuation of the tail between its transport, dock-loading and ground-loading positions is carried out through a single hydraulic power apparatus, preferably a single hydraulic cylinder. Such use of a single cylinder as the prime mover for manipulating the tail is made possible by making the undercarriage shiftable fore-and-aft of the main deck and its tail and by using such motion of the undercarriage to actuate the tail between its various positions.
The undercarriage has a relatively long path of travel which extends from a rearmost roading position of the undercarriage in which the ground wheels are fully under the tail to a forwardmost position of the undercarriage in which the ground wheels are almost entirely ahead of the hinge. Approximately the first half of the path of travel forward of the roading position is a lost motion segment during which the tail remains level. As the undercarriage moves beyond the halfway point, it clears the way for the tail to hinge downwardly by gravity toward the ground-loading position. Follower rollers on the rear end of the undercarriage roll up into parabolic pockets on the underside of the tail as the undercarriage moves forwardly, guiding and controlling the descent of the tail to the ground. To raise the tail back to its level, transport position, the undercarriage is returned toward the rear, during which rearward movement the tail is cammed back up to transport height. This raising movement can also be used to lift heavy loads situated on the tail.
A sturdy bumper assembly located beneath the tail extends horizontally rearwardly from the undercarriage when the tail is in its level transport position but yields to the downward force of the tail when the tail moves down to its ground-loading position, the bumper assembly being spring-loaded to provide such yielding during downward movement of the tail and to automatically return to a horizontal mode as the tail is re-established in its level condition.
The lost motion segment of the path of travel of the undercarriage can also be used for actuating the tail between its transport and dock-loading positions. To raise the tail to dock height, the undercarriage is first shifted forwardly to the forward limit of the lost motion segment. Then, a lifting strut, which is normally maintained down in a disabled position, is raised by an air bag actuator up into an enabled position in which it engages a socket on the underside of the tail. When the undercarriage is thereafter shifted rearwardly, such motion causes the lifting strut to push the tail upwardly until it reaches dock height. The strut then supports the tail in that position during onloading and offloading from the dock.